MQTT broker

The MQTT broker driver runs an MQTT broker on the YTCC server. Devices and other systems connect to it, publish messages and subscribe to topics, without a separate broker installation. For what all drivers have in common, see How drivers work.

The broker passes messages between its clients. To get the messages into YTCC, add an MQTT client driver that connects to this broker.

Protocol and role

Role	MQTT broker. Clients connect to YTCC.
Version	MQTT 3.1.1 over TCP
Listens on	All network interfaces of the server, port 1883 by default
Devices	None. The broker is a driver without devices.
Driver type	Mqtt server (mqtt_server)

Parameters

Set these on the driver in Drivers → devices. Changes take effect only after the driver restarts: Apply shows requires a restart, and a strip offers Restart for the driver. While it restarts, all clients are disconnected and reconnect by themselves. Messages and sessions are kept in memory; a restart of the driver clears the retained messages.

Parameter	Default for a new broker	Meaning
Port	1883	TCP port, 1–65535.
Max connections	10000	Most clients at the same time.
Max payload size	262144	Largest message in bytes (256 KB).
Allow anonymous	off	Allow clients to connect without a user.
Users	one user ytcc with a random password	User names and passwords for clients, as a JSON list: [{"user": "gw1", "password": "…"}].

A broker created in the editor starts with Allow anonymous off; keep it off. With Allow anonymous off and no users, no client can connect.

Security

• Users. Give each device or system its own user and password, and the MQTT client driver of YTCC its own user too. Every user can publish and subscribe to every topic, so create a user only for systems that you trust with every topic.
• Passwords. The passwords are part of the driver settings, so restrict who may edit the configuration.
• Network. Keep the broker and its clients in a protected network. The broker listens on every network interface: allow port 1883 (or your port) only from the devices that need it, with the firewall of the server.

Connecting

• Devices connect to <YTCC server>:1883 with their user and password.
• YTCC reads the messages with an MQTT client driver: as its device, set Host to the address of the server (for example 127.0.0.1 on the same server), Port to the port of the broker, and Username and Password to a user of the broker.

Diagnostics

Symptom	Likely cause
The broker does not start	The port is used by another program or another broker
Clients are refused	Wrong user or password, or Allow anonymous off for a client without a user
Clients connect, messages are missing	The message is larger than Max payload size, or the topics differ
A change has no effect	The driver has not been restarted